1. Field of the Invention
The present invention relates to a frit containing substantially no lead, having a thermal expansion coefficient (hereinafter, referred to as “α”) of at most 50×10−7/° C., and being processable at 500° C. or lower. The unit “%” used in the specification represents “mol %”.
2. Discussion of Background
Heretofore, as a frit to be used for materials such as kovar, alkali-free glass and silicon having α of at most 50×10−7/° C., a glass powder containing SiO2—B2O3 as a main component is used as disclosed in JP-A-09-110467. However, since the processing temperature of such glass exceeded 500° C., there were problems that other parts such as electrodes were damaged at the time of firing, and the thermal energy cost was high.
Further, in a case where only sealing is intended, e.g. JP-A-2005-191516 discloses a method of using a solder made of an Au—Sn alloy However, there were cost problems at the time of sealing a wide range since such an alloy was expensive in material cost as compared with a frit, and further there was a problem that the solder could not be used as a material for electrical insulation.
Further, JP-A-2002-164165 discloses a sealing method in which an organic material containing an epoxy resin as a main component is used. However, there was a problem that the resin was insufficient in air tightness in atmospheric air since e.g. moisture or carbon dioxide gas in an atmospheric air readily permeated the resin, and the reliability of the device tended to be lower than the case of using a frit.
In order to solve such problems, it has been desired to develop a frit having high electrical insulation characteristics and air tightness in atmospheric air, containing no lead, and being processable at a temperature of 500° C. or lower.
Patent Document 1: JP-A-09-110467
Patent Document 2: JP-A-2005-191516
Patent Document 3: JP-A-2002-164165
Patent Document 4; JP-A-2003-146691